The present invention relates to an apparatus for measuring the flow of a liquid, in particular urine, from a patient. More particularly, the invention relates to an apparatus of the type which comprises a measuring container having a bottom wall, a top wall and side walls and having an inlet opening for the liquid and adapted to define a state of maximum filling in which a liquid-empty part of the container has a smallest volume, and which also comprises means for emitting a first acoustic signal to the liquid-empty part of the measuring container, means for recording a second acoustic signal generated in the measuring container in response to the first signal, and means for determining a current amount of liquid in the measuring container on the basis of the second acoustic signal.
The invention also relates to a method of measuring the flow of a liquid, in particular urine, from a patient. The method uses an apparatus comprising a measuring container having a bottom wall, a top wall and side walls and having an inlet opening for the liquid and adapted to define a state of maximum filling in which a liquid-empty part of the container has a smallest volume, and which also comprises means for emitting a first acoustic signal to the liquid-empty part of the measuring container, means for recording a second acoustic signal generated in the measuring container in response to the first signal, and data processing electronics for determining a current amount of liquid in the measuring container via activatable connecting means, and which has a larger volume relative to the measuring container, said connecting means being adapted to allow draining of the measuring container in the state of maximum filling.
U.S. Pat. No. 4,658,834, e.g., already discloses an apparatus of this type. However, it is a common feature of the known apparatuses that they are relatively large, and that they moreover require a specially constructed apparatus housing to ensure correct operation of the apparatus. These inexpediencies as well as other problems are remedied according to the invention in that the measuring container has a measuring pipe having a first opening, a second opening and a third opening, said first opening being arranged to allow flow of the liquid into the measuring pipe to define a liquid surface in the measuring pipe, said second opening being arranged so as to communicate with the part of the measuring container empty of liquid at any time, said third opening being arranged so as to communicate with the means for recording the second acoustic signal, said second and third openings together with the surface of the liquid in the measuring pipe defining a liquid-empty resonance chamber to generate the second acoustic signal. By means of this apparatus, measuring may be performed in a quite particularly advantageous manner by using the so-called Helmholz resonator principle, and the apparatus is also unique e.g. by being more compact than other apparatuses which utilizes this principle.
By moreover providing the apparatus with an automatically operating draining mechanism which causes automatic draining of the measuring container under given circumstances, it is possible to manufacture an even more compact measuring container, which requires a very small volume for measurements to be performed. The draining mechanism may particularly advantageously be constructed wherein the connecting means comprise an automatically operating syphon mechanism adapted to provide draining of the measuring container in the maximum filling state, which provides an especially low cost solution.
The apparatus makes it possible to manufacture the measuring container with an optimum compactness, with the measuring pipe fully integrated in the measuring container. The apparatus also makes it possible to provide a solution in which the bacteriologically contaminated parts may be kept separated from the signal generating and receiving means as well as from the determining means, thereby allowing a distinction to be made between reusable components and disposable components.
When the measuring container is provided with the temperature correcting pipe utilizing the Helmholz Resonance principle, it is possible in a quite advantageous manner to compensate for temperature variations of the liquid which may otherwise give rise to incorrect measurements under certain circumstances.
The temperature correcting pipe is filled with a gas, which is preferably air.
The invention also relates to an advantageous method for providing accurate measurements in apparatuses which utilize the Helmholz resonator principle, and in which the measuring container is drained regularly, there being performed an estimation of the admission to the measuring container during the actual draining. A particularly expedient estimate may be performed wherein the estimate V is determined as V=(T*Atop+T*Bbottom)/2, where,T represents the duration of the draining.